Railway car retarder control with timed brake application

ABSTRACT

A speed-sensitive railway car retarder control system employing a plurality of vibration transducers mounted on a rail extending through the retarder, with speed determination based upon frequency of the signals generated by the transducers; a timed application circuit, preferably actuated by the signal from the transducer nearest the entrance end of the retarder, sets the retarder to braking condition for a given time interval whenever a new car enters the retarder, with the corresponding timed retarder operation for a stalled car.

United States Patent [72] Inventors Appl. No. Filed Patented Assignee [54] RAILWAY CAR RETARDER CONTROL WITH 3,240,930 3/1966 Porteretal.

Primary Examiner-Arthur L. La Point Assistant Examiner-George H. Libman Attmeyl(inzer, Dom and Zickert ABSTRACT: A speed-sensitive railway car retarder control system employing a plurality of vibration transducers mounted TIMED BRAKE APPLICATION on a rail extending through the retarder, with speed deter- 8 Claims, 3 Drawing Figs. mination based upon frequency of the signals generated by the 246 182A a application circuit prefflably actuated 4 1/04 by the signal from the transducer nearest the entrance end of Fieid 246/182 A the retarder, sets the retarder to braking condition for a given 104/26 time interval whenever a new car enters the retarder, with the corresponding timed retarder operation for a stalled car. [56] References Cited UNITED STATES PATENTS 3,166,278 l 1 965 Steinhach et al. 246/182 A 3 I L35 1 4 A [6 I34 I f & I & EIIIIIIIIIIIIJTITHTI) HlllIIlIIIIlIIIIlllHIIIIIIHIIIIIIIIHIIIIIIIIIIIHIIIIlIlIIHll llllwlllllllllllll & V75 IJA q 5 05/ l i k ACTUATING MPLI IER RESET 22 'i A F /*/9 CIRCUIT MECHAN SQUELCH 26 h i AMPL'F'ER 25 27 g 28 B EQUALIZER COMPRESSOR CL C|RCU|T AMPLIFIER GATE LOW PAss' FILTER LEWHFS Fl LTER as 52 48 Z RECTIFIER *L'fggg 6 EE??? RECTIFIER AMPLIFIER CONTROL e5 65 72 n 7 r57 5/ 55 CONTROL 55 AC 1 AC. 8 D

RAILWAY CAR RETARDER CONTROL WITH TIMED BRAKE APPLICATION CROSS REFERENCES TO RELATED APPLICATIONS The control system of the invention is applicable to the speed-sensing apparatus described in the pending application of Rosser L. Wilson Robert W. Convey and Earl E. Frank, Ser. No. 853,129, filed Aug. 26, 1969.

BACKGROUND OF THE INVENTION In the operation of a railroad classification yard, individual cars or cuts of cars are released from the top of an inclined hump and roll down the incline into the branching classification tracks in the yard. Braking may be required along the main feeder track, on the individual classification tracks, or on both. Successful commercial systems for controlling the car retarders employed in operations of this kind are described in U.S. Pat. No. 3,240,930 to Richard E. Porter and Arthur R. Crawford, issued Mar. 15, 1966. In the systems described in the Porter et al. patent, the speed of the moving cars is determined by sensing the vibration of a rail along which the cars move, the rail being provided with regularly spaced notches or other discontinuities so that it vibrates at a frequency representative of the speed of a car moving over the rails.

The various systems described in the Porter et al. patent can tolerate considerable extraneous vibration, which may be caused by switching along the railway near the retarder and by other sources not related to the car speed. Furthermore, the systems described in the patent can tolerate considerable variations in car wheels, such as flat spots, that cause pounding" on the rails resulting in vibrations that are picked up by the system transducers. Occasionally, however, a car is encountered that has one or more badly pitted or otherwise deformed wheels. Such a car may cause the rail to vibrate at a frequency corresponding to a low car speed, even when the car is actually moving at a much higher speed. As a result, the retarder control system may operate erroneously to permit a car to pass through the retarder without braking, although braking is definitely needed. This can produce a potentially dangerous situation.

A particular difficulty is created if a car with badly deformed wheels moves toward the retarder at a very short interval behind a normal car. Under these circumstances, even if the retarder is generally able to distinguish between the signals from normal cars and those from a car having deformed wheels, a confused operation may result. Again, if this confusion of operation permits a car to pass through the retarder unbraked, at high speed, a potentially dangerous condition is created.

SUMMARY OF THE INVENTION A principal object of the invention, therefore, is to minimize or eliminate the possibility of passing a car unbraked through a railway car retarder having a control system actuated by vibration of a rail extending through the car retarder, even though the car may have very badly pitted or otherwise deformed wheels. A principal feature of the invention is to provide automatic braking for a limited time only on all cars passing through the retarder, regardless of the entrance speed of the cars.

A specific object of the invention is to provide timed application means for actuating a speed-sensitive railway car retarder control system to maintain the car retarder in braking condition for a limited time interval each time a new car enters the car retarder.

A further object of the invention is to provide for initial timed application of a car retarder, normally controlled by a speed-sensitive control system, to brake each new car for a limited time interval, without effecting a corresponding timed application of a car retarder on a car that stalls in the retarder and subsequently resumes its rolling movement through the retarder, or on a car that is braked below release speed but subsequently accelerates above release speed.

A specific object of the invention is to provide an economi' cal and reliable timed application means for operating a vibra tion-actuated speed-sensitive railway car retarder control system to place the car retarder in braking condition for a preselected short time interval each time a new car enters the car retarder.

Accordingly, the invention is directed to a speed-sensitive railway car retarder control system comprising a rail extending into a car retarder and having a series of equally spaced surface discontinuities along a wheel-engaging surface of the rail. A plurality of vibration-sensitive transducers are mounted on the rail; the transducers develop initial electrical signals having frequencies representative of the velocity of a car moving along the rail. These initial electrical signals are combined, in a signal combining means, to develop a control signal having a frequency representative of car speed. Control means are provided for actuating the car retarder between its braking and released conditions in response to variations in the frequency of the control signal above and below a critical frequency representative of a given release velocity. A timed application circuit means is connected to the signal combining means and to the control means and operates to condition the control means to actuate the car retarder to braking condition for a predetermined limited time interval whenever a car en ters the retarder, regardless of the frequency of the control signal.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic plan view and block diagram of a control system for a railway car retarder, constructed in ac cordance with one embodiment of the present invention;

FIG. 2 is a detail schematic diagram illustrating several specific circuits for the retarder control system of FIG. 1; and

FIG. 3 is a detail schematic diagram of additional specific circuits for the system of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a railway car retarder control system I0 constituting a preferred embodiment of the present invention. The car retarder controlled by system 10 includes two sets of retarder rails 13A and 13B that are located immediately adjacent each other longitudinally of a traffic rail 11 (the other traffic rail for the railway is not illustrated). The retarder rails, however, are controlled from a common retarder actuating mechanism 15. A single set of retarder or brake rails may be used if desired.

Rail 11 is provided with a multiplicity of equally spaced shallow grooves or other surface discontinuities 16, beginning at a point 11A at the entrance end of the retarder ahead of the retarder rails 13A and 13B and ending at a point 118 at the outlet end of the retarder. The surface notches or grooves 16 need not be provided in the rail 11 along which the retarder rails 13A and 13B are mounted; rather, the corresponding length of the other traffic rail of the railway may be provided with the requisite notches or other surface discontinuities. Alternatively, a separate elongated notched sensing rail can be provided, in position to be engaged by a wheel moving along the traffic rail, as disclosed in the pending application of Rosser L. Wilson Robert W. Convey, and Earl E. Frank, Ser. No. 853,129,filed Aug. 26, I969.

Control system 10 includes three individual pickup devices 17A, 17B and 17C each comprising a vibration transducer mounted on rail 11. These pickup devices may be essentially similar in construction to conventional microphone pickups or other known vibration transducers. The initial pickup 17A is located near the point 11A at which the individual cars or cuts of cars enter the retarder. Pickup 17B is located within the length of traffic rail 11 encompassed by the first pair of retarder rails 13A. Pickup 17C is located near the outlet end of the retarder on the portion of the traffic rail encompassed by the second pair of retarder rails 13B. Pickup units 17A, 17B and 17C are all electrically coupled to an adder amplifier I9 that combines and amplifies the three initial electrical signals from the pickup devices 17A, 17B and 17C to produce a control signal.

Control system includes a squelch circuit comprising an amplifier 22 having its input coupled to the output of adder amplifier 19. The output of squelch amplifier 22 is coupled to a rectifier and drive circuit 23. Drive circuit 23 energizes the operating coil 24 of a squelch relay 25.

RElay 25 comprises four sets of contacts, shown in their normal, unenergized positions. The first set of contacts comprises two fixed contacts 26 and 27 and a movable contact 28, movable contact 28 normally being engaged with contact 26. The second set includes a movable contact 31 normally engaged with a fixed contact 29 but movable to engagement with another fixed contact 30. The next set includes a fixed contact 32 normally engaged by a movable contact 34, movable contact 34 engaging a second fixed contact 33 when the relay is energized. The fourth set of contacts for the squelch relay comprises a movable contact 36 that is normally engaged with a fixed contact 38 but which engages a second fixed contact 37 upon energization of the relay.

The output of adder amplifier 19 is also coupled to an equalizer circuit 42. The equalizer circuit, which is utilized to compensate for the frequency characteristics of the pickup devices 17A, 17B and 17C, is in turn coupled to a compressor amplifier 43. Compressor amplifier 43 is also provided with a connection to the contacts 26 of squelch relay 25 to modify the operating characteristics of the compressor amplifier upon actuation of the squelch relay.

The output of compressor amplifier 43 is coupled to a clipper gate 45. Gate 45, in turn, is connected through a selector switch 44 to the input of a low-pass filter 46. Low-pass filter 46 is constructed as a fixed filter; changes in the critical release speed for the retarder control system are effected by switching from one filter circuit to another. Thus, a second low-pass filter 46A, having a different cutoff frequency from filter 46, can be substituted in the operating circuit by actuation of a pair of connecting switches 44 and 44A. Although only two low-pass filters are illustrated in FIG. 1, it should be understood that several additional filter circuits may be employed with appropriate means for switching from one filter to another to establish different desired levels for the critical release speed of the retarder system.

Low-pass filter 46 is coupled through selector switch 44A to a drive amplifier 47 that is in turn connected to a rectifier 48. Rectifier 48 is utilized to charge a control capacitor 51. Capacitor 51 is coupled to a release relay control circuit 52, utilized to energize the operating coil 55 of a release relay 56.

Release relay 56 includes four sets of contracts, all shown in the normal or unenergized condition for the relay. The first set of contacts comprises a movable contact 57 normally engaged with a fixed contact 58 but engageable with a second fixed contact 59 when the relay is energized. The second set of release relay contacts includes a movable contact 61 normally engaged with a fixed contact 62 but movable into engagement with a second fixed contact 63. The third set of contacts for the release relay includes a movable contact 65 normally engaged with a fixed contact 66 and engageable with a second fixed contact 67 upon energization of the relay. The fourth set of contacts comprises a movable contact 68 movable from a fixed contact 69 to a fixed contact 70 upon energization of the relay.

In addition to the connection to clipper gate 45, compressor amplifier 43 is provided with an output connection to a highpass filter amplifier 71. This circuit includes, in series, the fixed contact 58 and the movable contact 57 in the first set of contacts of release relay 56. The remaining contact 59 in this set is left open-circuited.

The output of high-pass filter amplifier 71 is coupled to a rectifier circuit 72 which is in turn coupled to an application relay control circuit 73. The input to control circuit 73 also includes a connection to the fixed contact 29 of squelch relay 25. The related movable contact 31 of the squelch relay is returned to system ground, whereas the remaining fixed contact 30 in this set if left open-circuited.

Control circuit 73 is utilized to actuate a retarder application relay 75, being connected to the operating coil 76 of the relay. Application relay 75 includes two sets of contacts. The first set comprises an open-circuited fixed contact 77 normally engaged by a movable contact 78, the contact 78 moving into engagement with a second fixed contact 79 upon energization of the relay. The second contact set in the application relay comprises a fixed contact 81 that is normally engaged by a movable contact 82, the movable contact being engageable with a second fixed contact 83 upon actuation of the relay.

In application relay 75, fixed contact 81 is returned to system ground through a resistor 85. Movable contact 82 is connected to a capacitor 86 that is returned to ground. Contact 83 is connected back to control circuit 73.

The remaining set of contacts in application relay 75 are interconnected with the contacts of release relay 56 in a control circuit for a brake relay 21. Thus, the fixed contact 79 of application relay 75 is directly connected to brake relay 21. The fixed contact 77 is left open-circuited but the movable contact 78 is connected to the fixed contact 66 in the release relay 56. The related movable contact 65 is connected directly to brake relay 21, whereas the remaining fixed contact 67 is open-circuited. Brake relay 21 is connected to actuating mechanism 15 as indicated by circuit 18.

Release relay contacts 68-70 form a part of the input circuit for application relay control 73. Thus, movable contact 68 is connected to system ground, normally closed contact 69 is left open-circuited, and normally open contact 70 is connected to the input to control 73.

Returning to squelch relay 25, it is seen that movable contact 28 is connected to a positive DC supply, designated B The normally closed contact 26 is connected to the compressor amplifier 43; contact 27 is open-circuited. Movable contact 34 is connected to a capacitor 39 that is returned to system ground. The normally closed contact 32 is connected to a resistor 40 that is returned to ground. The normally open contact 33 is connected to the drive circuit 23.

The remaining contacts of the squelch relay 25 and the release relay 56 are incorporated in a timed brake application circuit that includes a quick reset circuit 89. The quick reset circuit 89 has an input derived from the first pickup transducer 17A. The output of circuit 89 is connected to the normally closed contact 38 in squelch relay 25. The movable contact 36 is connected to a timing capacitor 41 that is returned to system ground. The normally open contact 37 is connected to the movable contact 61 in release relay 56. The normally closed contact 62 is connected to gate 45. The normally open contact 63 is connected, through a resistor 88, to the B.+

. pp y- With control system 10 in operation, but with no car on traffic rail 11, retarder actuating mechanism 15 maintains the retarder rails 13A and 133 in their open or released positions. For a braking operation, actuating mechanism 15 is energized from brake relay 21. But the operating circuit for brake relay 21 is open at contacts 77 and 79 of noise relay 75. Accordingly, the retarder remains in its released condition until the brake relay is actuated by control system 10.

An approaching car or cut of cars entering the retarder in the direction of arrow A first engages the notched portion of rail 11 at point 11A. Continuing movement of the car causes the rail to vibrate at a frequency determined by the velocity of the car and by the spacing of the rail notches 16. Vibration of the rail is detected by pickup devices 17A, 17B and 17C and the initial electrical signals from the three pickups are additively combined in amplifier circuit 19 to produce a control signal. At the outset, as the first wheels of the cut pass point 11A, the signal from pickup 17A predominates.

The signal from adder amplifier 19 is applied to squelch amplifier 22 and to equalizer circuit 42. Referring to squelch amplifier 22, the control signal from amplifier 19, is amplified further and then applied to the rectifier and drive circuit 23.

Circuit 23 energizes relay 25, actuating movable contacts 28, 31, 34 and 36 to their alternate operating positions, closing upon fixed contacts 17, 30, 33 and 37 respectively. Circuits 22 and 23 are arranged to energize relay 25 only if the control signal from amplifier 19 lasts long enough to indicate the probable presence of a car.

The closing of contacts 33 and 34 in squelch relay 25 connects capacitor 39 into rectifier drive circuit 23. Connecting the capacitor into the rectifier and drive circuit 23 assures a sustained output signal from circuit 23 to hold squelch relay 25 energized long enough to preclude chattering of the relay in the event of momentary subsequent interruption of the control signal immediately following energization of the relay.

The opening of contacts 26 and 26 in squelch relay 25 opens a bias circuit in compressor amplifier 43, disconnecting the Brisupply from the compressor amplifier and materially increasing the gain of the compressor amplifier. This circuit connection prevents development of a high-amplitude output signal from the compressor amplifier in response to short duration signals and transients such as might be caused by switching at a nearby location, by the driving of spikes at some adjacent point along the line, or by other sources. The gain of compressor amplifier 43 is held to a minimal level when there is no car actually moving along the notched rail 11, but is increased to a desired operating level once a signal of sufficient duration is available to actuate squelch relay 25. In this regard, it should be noted that the rectifier and drive circuit 23 may utilize a conventional diode pump" circuit to afford a predetermined time delay in actuation of the squelch relay.

The control signal from adder amplifier 19 is also translated through equalizer circuit 42 and applied to the input of compressor amplifier 43. In conventional vibration pickup devices, the amplitude of the signal output increases appreciably with increasing frequency. In operation of control system 10, it is important to sense and detect the low-frequency range of the output signals from the pickups in order to assure release of a car moving through the retarder before it is completely stopped. Equalizer circuit 42 is effective to increase the amplitude of the low-frequency components relative to the amplitude of the high-frequency components and thereby correct for the normal operating characteristics, with respect to frequency, of the pickups. Stated differently, equalizer circuit 42 functions as a bass-boost circuit, emphasizing the low-frequency portion of the input signals to compressor amplifier 43.

One output connection from compressor amplifier 43 is supplied to high-frequency filter amplifier 71 through the application relay contacts 57 and 58. The output signal from amplifier 71 is rectified in circuit 72 and supplied to control 73 to energize application relay 75. When the application relay is energized, the operating circuit for brake relay 21 is completed by the closing of the relay contacts 78 and 79, actuating the retarder to braking condition.

The output circuit from rectifier 72 to control circuit 73 is normally grounded through the connection to contacts 29 and 31 of squelch relay 25. Accordingly, no effective actuating signal can be supplied to application relay control circuit 73 as long as the squelch relay 25 remains unenergized. This presents no difficulty with respect to an incoming car on traffic rail 11, since the squelch relay is promptly actuated when the car reaches the notched portion of rail 11 as described above.

In some instances, however, it is necessary to release the the retarder rapidly in the course of a braking operation. For example, a light car moving into the retarder may be braked so rapidly that there is insufficient time to release the retarder through the operation of the low-frequency signal channel, described hereinafter, prior to the time that the car stops. But when the car stops, squelch relay 25 drops out because there is no longer a sustained signal from drive circuit 23 to keep the relay in operation. When the squelch relay drops out, contacts 29 and 31 close and again ground the coupling circuit between rectifier 72 and control circuit 73, deenergizing application relay 75. This promptly releases the retarder, since the operating circuit for brake relay 21 is opened at contacts 76 and 79 in the application relay.

As long as the initial signals developed by the three pickup devices remain relatively high in fundamental frequency, indicating a rapidly moving car, the retarder remains in actuated braking condition as described above. Because the signal is relatively high in frequency, there is no more than a negligible output from filter 46 and hence virtually no output signal supplied from drive amplifier 47 to rectifier 48.

When the car is slowed down sufficiently so that the signal transmitted through circuits 43, 45 and 46 is below the cutoff frequency of low-pass filter 46, an appreciable output signal is developed by drive amplifier 47. This output signal from the drive amplifier is rectified in circuit 48. The output of rectifier 43 charges capacitor 51 and actuates the release relay control circuit 52 to energize release relay 56. When this occurs, contacts 65 and 66 open to break the operating circuit for brake relay 21 and release the retarder. At: the same time, contacts 57 and 56 open, interrupting the energizing circuit for application relay 75 and causing that relay to drop out. The operating circuit for brake relay 21 is accordingly opened at relay contacts 78 and 79.

If the car speeds up while still in the retarder but after the retarder has been released, the frequency of the signals developed by the pickup devices may again increase to a level at which the signal cannot be passed through low-pass filter 46. When this occurs, release relay 56 drops out, since there is an insufficient actuating signal output from rectifier 48 to control circuit 52. When relay 56 drops out, it is again possible to actuate the application relay 75 through its usual input circuit comprising the relay contacts 57 and 58 and the circuits 71, 72 and 73. Accordingly, the application relay is again actuated, closing contacts 78 and 79 to energize brake relay 21 and again actuate retarder mechanism 15 to braking condition.

The operation of retarder control system 10, as thus far described, corresponds generally to the control systems disclosed in Porter et al. US. Pat. No. 3,240,930. The control systems of the patent, although highly effective and efficient in most operations, are susceptible of erroneous operation, on occasion, upon entry of a car having one or more badly deformed wheels. Specifically, an entering car having one or more pitted or otherwise deformed wheels that create a lowfrequency vibration in the rail on which the transducers 17A and 17C are mounted may cause the transducers to produce output signals indicating that the car is travelling at a much lower speed than is actually the case. if the pounding of a deformed wheel on the rail produces vibrations of greater amplitude than those caused by engagement of the wheel with the notches 16, the retarder control may operate to allow the car to pass without braking. This can create a potentially dangerous situation.

In control system 10, errors of this kind are eliminated by the provision of a timed application circuit connected to the adder amplifier 19 and to the basic control circuits of the system. in FlG. 1, the timed application circuit comprises the contacts 3643 of squelch relay 25,. the timing capacitor 41, the contacts 61-63 of the release relay 56, and the quick reset circuit 89. This timed application. circuit enables control system 10 to brake any and all cars that enter the retarder, re gardless of entry speed, for a given limited time interval. That is, the control circuits of system 10 are actuated to place the car retarder in braking condition for a predetermined limited time interval whenever a new car enters the retarder.

Whenever there are no appreciable signals from the pickups 17A through 17C, timing capacitor 41 is connected, through the normally closed relay contacts 36 and 38, to a DC charging circuit that is included in the quick reset circuit 39. If a fixed charging circuit is employed, the timing capacitor 41 is slowly charged to a given DC level. When a car enters the retarder and squelch relay 25 is energized, as described above, the connection of the timing capacitor 41 to its charging circuit, through contacts 36 and 38, is broken. Instead, the timing capacitor is connected through relay contacts 36 and 37 and through the normally closed contacts 61 and 62 of release relay 56 to the clipper gate 45.

The charge on timing capacitor 41, as applied to gate 45, actuates the gate to a closed or off" condition. Consequently, although the signals derived from pickups 17A through 17C are supplied to amplifier 19 and the control signal from amplifier 19 is applied through the high-frequency channel 42, 43, 71, 72 and 73 to actuate application relay 75, that portion of the signal which would normally be supplied to one of the lowpass filters 46 and 46A is cut off. It is thus seen that the application relay 75 is actuated under circumstances in which release relay 56 cannot be actuated. As a consequence, the operating circuit for brake relay 21 is completed through the relay contacts 65, 66, and 78, 79.

This operating condition is maintained only for the time required to discharge timing capacitor 41. As the capacitor discharges, the bias signal supplied to gate 45 drops to a point at which the gate is no longer held in closed condition. Accordingly, gate 45 opens and the control signal is supplied to the operational low-pass filter and may actuate the release relay to release the retarder, as described above, if the control signal frequency is low enough to indicate a safe release speed.

The net effect of this timed application circuit, comprising capacitor 41, is to maintain the retarder in braking condition from the time of entry of a car into the retarder until after a predetermined time interval has expired, reverting to normal speed control upon expiration of the selected time interval. When the car passes out of the retarder, and the relays are all deenergized, timing capacitor 41 is again connected to its charging circuit. A relatively long charging time constant may be chosen to provide for the possibility of a car being stalled within the retarder. If a stall occurs, all relays drop out, due to loss of vibration signals at the transducers 17A-17C, and a second timed application of the retarder could occur when the car starts to roll. The long charging time prevents charging of timing capacitor 41 to a significant voltage during the short duration of a stall; for example, a charging time of twenty seconds may be employed, assuring a full recharge between cars without substantial possibility of a second timed application of the retarder in the event of a stall.

After the selected time interval established by capacitor 41 has expired and control system reverts to its speed-sensitive mode of operation, the first time the car speed drops to or below the desired release speed, the release relay 56 is energized, releasing the retarder by opening contacts 65 and 66 as described above. When this occurs, contacts 61 and 63 are also closed, connecting timing capacitor 41, through resistor 88, to a DC source of opposite polarity from the charge normally applied to the capacitor to affect the timed application of the retarder described above. For the specific circuit shown in FIG. 1, capacitor 41 is charged'to a negative polarity to carry out the timed application of the retarder. Consequently, resistor 88 is connected to the B supply. By charging capacitor 41 to an opposite polarity in this manner, upon release of the retarder as the result of sensing of a low-speed condition, the charging time for capacitor 41 is materially increased, lending further assurance that there will be no repetition of the timed application of the retarder in the event of a stall.

From the foregoing operational description of the timed application circuit comprising capacitor 41, it will be recognized that the timing capacitor can be connected in a fixed charging circuit. If this is done, however, and two cars enter the retarder within a relatively short time interval, only the first car is subjected to the timed application of the retarder because there is not sufficient time for capacitor 41 to recharge. For example, two cars following each other with a time differential of ten seconds or less will not allow the timed application circuit to recover soon enough to afford an initial automatic braking period for the second car. If it happens that the second car has badly deformed wheels, as discussed above, it may be permitted to go through the retarder without adequate braking.

This difficulty is overcome by means of the quick reset circuit 89, which affords a means to charge capacitor 41 quickly while at the same time avoiding the possibility of multiple reapplications of the retarder on a separate car.

Quick reset circuit 89 is generally similar to squelch amplifier 22 in its operation, but receives its input only from the first transducer 17A at the entrance end of the retarder. The preferred circuit, described more fully hereinafter, comprises an amplifier, a capacitively coupled DC pump that produces a DC voltage whenever a signal is available from pickup'17A, and a relay driver that energizes a reset relay.

When a car enters the retarder and an initial signal is developed by pickup transducer 17A, the relay in quick reset circuit 89 is energized. The quick reset circuit is arranged to energize its reset relay before squelch relay 25 is energized. Closing of the reset relay connects a rapid charging circuit to capacitor 41, quickly charging the capacitor to the required voltage to provide a timed application of the retarder as described above. The timed application is actually initiated by energization of squelch relay 25. When the car passes beyond the range of the first vibration pickup 17A, the relay in quick reset circuit 89 drops out so that the timing capacitor 41 cannot be recharged again until a significant signal is generated by pickup 17A. Squelch relay 25, on the other hand, remains energized by signals from the subsequent pickup transducers 17B and 17C so that the speed control circuits function in the normal manner described above. If a car stalls in the retarder and all relays drop out, the quick reset relay in circuit 89 will not be reenergized when the car subsequently starts to move again, unless the car stalls over the first pickup. Consequently, and particularly since almost all stalls occur with the car well into the retarder, a second timed application of the track retarder does not occur. Only a second incoming car will reinitiate the timed application of the retarder.

With a quick reset circuit as described, timing capacitor 41 can be recharged rapidly instead of at the slow rate necessary with a fixed charging circuit. This enables effective use of control system 10 in circumstances in which cars may follow each other into the retarder with minimum permissible spacing, defined as the spacing which just allows one car to leave the retarder before the next car enters. Even with minimum permissible spacing, each car receives the desired timed application of the retarder to insure limited braking of all cars.

FIGS. 2 and 3 illustrate, in detailed schematic form, typical circuits that may be utilized for a number of the components of control system 10. As shown in FIG. 2, pickup 17A is coupled through a capacitor 101 to a resistor 104 that is returned to system ground. Capacitor 101 is also coupled, through a capacitor 105 and a series resistor 106, to a terminal 107 that is connected to the base electrode of a transistor 108. Terminal 107 is also returned to ground through an input resistor A similar circuit arrangement is used for pickup 17 B, which is coupled through a capacitor 111 to a resistor 114 that is returned to ground. Capacitor 111 is also coupled through a capacitor 115 and a series resistor 116 to terminal 107. An identical arrangement is used for pickup 17C.

Transistor 108 is connected in a conventional feedback amplifier configuration. The emitter of the transistor is returned to ground through a resistor 117 that is bypassed by a capacitor 118. The collector of transistor 108 is connected to the C- supply by a load resistor 119 and is also connected back to the base by a feedback circuit comprising the parallel combination of a capacitor 120 and a resistor 121.

The next stage in adder amplifier 119 comprises a transistor 122 having its base connected to the collector of transistor 108 by a resistor 130. A capacitor 113 is connected from the base of transistor 122 to ground. Transistor 122 is connected in an emitter-follower circuit. The collector is connected to the C- supply by a limiting resistor 112. The emitter of transistor 122 is returned to ground through a load resistor 123. The output to equalizer circuit 42 is taken through a capacitor 124 connected to the emitter of transistor 122. A reduced amplitude output is taken for squelch amplifier 22,

the second output circuit used for this purpose comprising a capacitor 125 and a potentiometer 126 connected from the emitter electrode of transistor 122 to ground. The circuit connection to squelch amplifier 22 is taken from the tap on potentiometer 126. A pair of oppositely polarized diodes 102 and 103 are connected from the tap of potentiometer 126 to ground.

Equalizer circuit 42 is quite simple in construction. It comprises a pair of coupling resistors 127 and 128 and a potentiometer 129 connected in series with each other from capacitor 124 to ground. A capacitor 131 is connected from the common terminal of resistors 127 and 128 to ground. A pair of diodes 132 and 134 are connected, in parallel and with reversed polarities, from the common terminal of resistors 127 and 128 to ground. A capacitor 133 is connected in parallel with potentiometer 129. The output connection from the equalizer to compressor amplifier 43 is made at the movable tap on potentiometer 129.

A conductor 141 connects the tap on potentiometer 126 of amplifier 19 to the input of squelch amplifier 22; the input circuit of the squelch amplifier comprises a capacitor 142 in series with a resistor 143 that is connected to the junction 144 of a voltage divider comprising a resistor 145 and a resistor 146 connected from the C- supply to ground. The voltage divider terminal 144 is connected to the base of a transistor 147 by a resistor 148. The emitter of transistor 147 is connected to ground through the parallel combination of a resistor 149 and a capacitor 151. The collector of transistor 147 is connected to the supply by a load resistor 152 and is coupled back to the base of the transistor by a feedback capacitor 150.

The output stage of squelch amplifier 22 is an emitter-follower comprising a transistor 153 having its base connected to the collector of transistor 147. The collector of transistor 153 is connected to the C- supply by a limiting resistor 154. The emitter of transistor 153 is connected to a load resistor 155 that is returned to ground.

The output connection from squelch amplifier 22 to the rectifier drive circuit 23 is provided by a capacitor 156 that is connected from the emitter of transistor 153 to the cathode of a diode 157 having its anode connected to ground. Capacitor 156 is also connected to the anode of a diode 158; the cathode of diode 158 is connected to a capacitor 161 that is returned to ground and is also connected to a resistor 159. The other terminal of resistor 159 is connected through a resistor 162 to the gate electrode of a signal-controlled rectifier 163. The anode of rectifier 163 is connected to one terminal of the operating coil 24 for the squelch relay 25, the other terminal of coil 24 being connected to an AC supply. The cathode of rectifier 163 is connected to system ground.

The rectifier-drive circuit 23 further includes two resistors 164 and 165 connected from the common terminal of resistors 159 and 162 to system ground. The junction of resistors 164 and 165 is connected to contact 33 of squelch relay 25.

Quick reset circuit 89, in the embodiment illustrated in FIG. 2, comprises a conductor 171 that is connected to the output of pickup 17A and is coupled by a capacitor 172 to a potentiometer 173 that is returned to system ground. The tap on potentiometer 173 is coupled by a capacitor 174 to the base of a transistor 175. The base of transistor 175 is also connected to a voltage divider comprising two resistors 176 and 177 connected from the B.+ supply to system ground. The emitter of transistor 175 is returned to ground through the parallel combination of a resistor 178 and a capacitor 179. The collector of transistor 175 is connected to the 8+ supply by a load resistor 181 with a feedback capacitor 182 connecting the collector back to the base of the transistor.

Circuit 89 includes a second stage comprising a transistor 183 having its base connected to the collector of transistor 175. The collector of transistor 183 is connected to the 8+ supply andthe emitter is connected to ground through a load resistor 184. The output from this stage of the quick reset amplifier comprises a capacitor 185 connected from the emitter of transistor 183 to the cathode of a diode 186 and the anode ofa diode 187. The anode of diode 186 is returned to ground and the cathode of diode 187 is connected to a resistor 188 that is in turn connected to the base of a gate transistor 189. The common terminal of diode 187 and resistor 188 is bypassed to ground by a capacitor 191..

Transistor 189 is connected in the energizing circuit for the operating coil 192 of a reset relay 193. Thus, one terminal of coil 192 is connected to the B+ supply and the other terminal of the coil is connected to the collector of transistor 189. The emitter of transistor 189 is grounded. A diode 194 may be connected across coil 192.

Reset relay 193 comprises a normally closed fixed contact 195, a normally open fixed contact 196, and a movable contact 197. Fixed contact 195 has no external connection. Contact 196 is connected to the C- supply. Movable contact 197 is connected, through a small resistor 198, to the fixed contact 38 of squelch relay 25.

FIG. 3 illustrates specific circuits usable for the clipper gate 45, rectifier 48, and release relay control 52 in the lowfrequency channel of the system. As shown therein, clipper gate 45 may include an input capacitor 201 connected to one output of compressor amplifier 43 and further connected to a resistor 202. The common terminal of capacitor 201 and resistor 202 is connected to a diode .203 that is returned to ground. The other terminal of resistor 202 is connected to a load resistor 240 that is returned to ground and to a coupling capacitor 205 that is in turn connected to the base of an output stage transistor 206. A gate transistor 207 is connected in parallel with load resistor 204; the collector of transistor 207 is connected to the common terminal of resistor 202 and capacitor 205, and the emitter of the gate transistor is returned to ground. The base of gate transistor 207 is connected to a resistor 208 that is in turn connected to the normally closed fixed contact 62 of release relay 56. Only a part of the release relay contacts are illustrated in FIG. 3.

In clipper gate 45, the collector of transistor 206 is con nected to the C- supply and the emitter is connected to a load resistor 209 that is returned to ground. The emitter of transistor 206 is connected to a feedback capacitor 211 that is returned to the base of the transistor through a resistor 212. A bias circuit is provided for transistor 206 in the form of a voltage divider comprising two resistors 213 and 214 connected from the C- supply to ground, with the common terminal of the two resistors 213 and 314 being connected to resistor 212.

The output circuit from clipper gate 45 to filters 46 and 46A comprises a coupling capacitor 216 connected from the emitter of transistor 206 to the select-or switch 44 in the input to the filters. A resistor 217 is connected from the output side of capacitor 216 to system ground.

The output stage of drive amplifier 47 is shown in FIG. 3; it comprises an emitter-follower including a transistor 221 having its collector connected to the C- supply and its emitter returned to ground through a load resistor 222. The emitter of transistor 221 is connected to a resistor 223 in series with a capacitor 224. Capacitor 224 is in turn connected to the cathode of a diode 225 and the anode of a diode 226. The anode of diode 225 is grounded and the cathode of diode 226 is connected to the capacitor 51 referred to above, capacitor 51 being returned to ground.

Capacitor 51 is also connected to the gate electrode of a signal-controlled rectifier 227, in release relay control 52, by the series combination of two resistors 228 and 229. The common terminal of resistor 228 and 229 is connected to a resistor 231. Resistor 231 is in turn connected to the center terminal of a voltage divider comprising two resistors 232 and 234 connected from the 0 supply to ground. The anode and cathode of rectifier 227 are connected to the operating coil 55 of release relay 56 and to ground respectively, coil 55 also being connected to the AC supply.

The general operation of the circuits of FIGS. 2 and 3 will be apparent from the foregoing description of the overall system 10 in which these circuits are incorporated. However, some of the operating characteristics of the preferred construction for the control system can be better understood by particular reference to the schematic circuits of FIGS. 2 and 3.

When a new car enters the car retarder (FIG. 1) the initial contact of the car wheel with the notched portion of rail 11 first produces a significant output signal from the first vibration transducer, pickup 17A (FIGS. 1 and 2). This initial electrical signal from the first transducer at the entrance end of the car retarder is supplied to the input of the amplifier in quick reset circuit 89. The signal is amplified, rectified in the diode pump circuit comprising diodes 186 and 187, and supplied to the base electrode of transistor 189 to drive the transistor to conductive condition. This completes an operating circuit for reset relay 193, energizing the relay and closing contacts 196 and 197. Consequently, the C- supply is connected to timing capacitor 41 through resistor 198, rapidly charging the timing capacitor to the full C- voltage. The charging time period for timing capacitor 41, using the main charging circuit comprising the C- supply, the contacts of relay 193, and resistor 198, is quite short and should be substantially less than one second in duration.

The initial electrical signal generated by the first pickup 17A is also applied to adder amplifier 19 and produces an output signal from the adder amplifier that is supplied, over circuit 141, to the input of squelch amplifier 22. The squelch amplifier utilizes this signal to actuate rectifier drive circuit 23 and energize squelch relay 25. However, as generally described above, squelch amplifier 22 and drive circuit 23 do not operate instantaneously; the input signal must endure for a given time interval before the SCR 163 is gated to conduction and the squelch relay is energized. The actuation time for squelch relay 25 is made substantially longer than the actuation time for reset relay 193, the differential being at least equal to the charging period for timing capacitor 41 so that capacitor 41 is fully charged before the squelch relay operates.

When squelch relay 25 is energized, its movable contact 36 switches from the normally closed fixed contact 38 to engagement with the normally open fixed contact 37. This opens the main charging circuit for timing capacitor 41 and connects the timing capacitor, through the contacts 61 and 62 of release relay 56 (FIG. 3) to the base electrode of the gate transistor 207 in gate 45. The voltage on the timing capacitor is thus applied to the base of the gate transistor 207, driving that transistor conductive and shunting the input stage of gate circuit 45. Consequently, although the output signal from adder amplifier 19 is applied to compressor amplifier 43 through equalizer 42 (see FIG. 1) it is not passed on to the lowfrequency signal channel comprising circuits 46, 47, 48 and 52. Stated differently, the voltage from timing capacitor 41 in the timed application circuit of the system is applied to the gate transistor in gate 45 to actuate the gate to a closed condition and prevent the control signal from adder amplifier 19 from reaching the low frequency'signal channel that can actuate the car retarder to released condition. I

The discharge time for timing capacitor 41 determines the time interval during which gate 45 is maintained in closed condition. This time interval may be varied, depending upon the physical conditions relative to the car retarder, such as the inclination of the hump at the retarder and other factors. As capacitor 41 discharges, it reaches a voltage level at which transistor 207 is no longer maintained conductive, thus opening gate 45. This conditions the low-frequency signal channel of the control system for operation to release the retarder when the frequency of the control signal indicates that the car is moving slow enough to be permitted to roll on to its destination.

When the car slows down to below the critical release speed, determined by the low-pass filter 46 or 46A in the lowfrequency channel of the control system, release relay control 52 is actuated to energize the operating coil 55 for signal relay 56 (FIG. 3). When release relay 56 is energized, its movable contact 61 is switched from engagement with fixed contact 62 into engagement with fixed contact 63. This opens the circuit connection from timing capacitor 41 FIG. 2) to gate 45 and at the same time completes an auxiliary charging circuit to the timing capacitor, through relay contacts 61 and 63 and through the connection of contact 63 to the B.+ supply. Consequently, capacitor 41 is charged to a positive potential. If the car subsequently speeds up enough to cause the control system to deenergize release relay 56, the positive charge applied to timing capacitor 41 by this auxiliary charging circuit materially increases the charging time for the capacitor and helps to prevent a possible timed reactuation of the car retarder as occurred when the car first entered the retarder. Thus, the auxiliary charging circuit assures maintenance of speed control only, once speed control has been established following the initial timed application of the car retarder.

In order to afford a more complete description of a preferred embodiment of the invention, certain parameters for the circuits of FIGS. 2 and 3 are set forth below. It should be understood that these data are furnished merely by way of illustration and in no sense as a limitation on the invention.

Resistors, Potentiometers 104,114,208 33 kilohms 106,116 39 kilohms 109,143,146 22 kilohms 88,117,178 470 ohms 121 220 kilohms 119,123,152,1B1,198 4.7 kilohms 40,112,154 ohms 126,165,177,188,202,209 l0 kilohms 130,145 180 kilohms 127,159,164,213,22l,231 47 kilohms 128,129,212,214,217 I00 kilohms 148,184 2.7 kilohms 149 l kilohm 155 2.2 kilohms 162,229 27 kilohms I73 50 kilohms 176 I50 kilohms 204 I5 kilohms 222 1.8 kilohms 223 820 ohms 234,232 9.1 kilohrns Capacitors 0.15 microfarad 0.22 microfarad 0.0033 microfarad 0.0l microlarad a rail extending into a car retarder and having a series of equally spaced surface discontinuities along a wheel-engaging surface thereof;

a plurality of vibration-sensitive transducers mounted on the rail for developing initial electrical signals having frequencies representative of the velocity of a car moving along the rail;

signal combining means for combining said initial signals to develop a control signal having a frequency representative of car speed;

control means for actuating the car retarder between braking and released conditions in response to variations of the control signal frequency above and below a critical frequency representative of a given release velocity;

said control means including a low-frequency signal channel for actuating the retarder to released condition and having a gate incorporated in said low-frequency channel;

and timed application circuit means, connected to said signal combining means and to said gate in said control means, for actuating said gate to closed condition, in response to said control signal, to maintain the car retarder in braking condition for a predetermined limited time interval every time a car approaches the retarder along said rail, regardless of the frequency of said control signal, said time interval being long enough to assure at least limited braking of any car entering the retarder above a preselected minimum speed.

2. A railway car retarder control system according to claim 1 in which said timed application circuit comprises a timing capacitor, a main charging circuit for charging said timing capacitor to a voltage of given polarity and predetermined amplitude, and squelch switching means for connecting said timing capacitor to said gate in said low-frequency channel each time a control signal is initiated.

3. A railway car retarder control system according to claim 2, in which said timed application circuit further comprises an auxiliary charging circuit for charging said timing capacitor to a voltage of opposite polarity, and in which said control means includes additional switching means, actuated by said lowfrequency signal channel, for connecting said auxiliary charging circuit to said timing capacitor whenever the car retarder is released by operation of said low-frequency signal channel, to preclude a timed reapplication of the car retarder to braking condition on a car that accelerates within the retarder after being braked below said release velocity.

4. A railway car retarder control system according to claim 2, in which said main charging circuit has a long recharge time, of the order of 20 seconds, to further preclude a timed reapplication of the car retarder on a stalled car.

5. A railway car retarder control system according to claim 2, in which said main charging circuit is energized in response to the initial electrical signal from the first of said transducers located at the entrance end of the car retarder and is deenergized in the absence of said initial electrical signal from said first transducer.

6. A railway car retarder control system according to claim 5, in which said main charging circuit has a short charging time period of the order of less than I second.

7. A railway car retarder control system according to claim 6, in which said main charging circuit comprises reset switching means for connecting said timing capacitor to a voltage supply of said given polarity and a reset amplifier having an input connected to said first transducer and an output connected to said reset switching means: for actuation thereof, said reset switching means having an actuation time shorter than the actuation time for said squelch switching means by at least said charging time period.

8. A railway car retarder control system according to claim 5, in which said timed application circuit further comprises an auxiliary charging circuit for charging :said timing capacitor to a voltage of opposite polarity, and in which said control means includes additional switching means, actuated by said lowfrequency signal channel, for connecting said auxiliary charging circuit to said timing capacitor whenever the car retarder is released by operation of said low-frequency signal channel,

to preclude a timed reapplication of the car retarder to braking condition on a car that accelerates within the retarder after being braked below said release velocity. 

1. A speed-sensitive railway car retarder control system comprising: a rail extending into a car retarder and having a series of equally spaced surface discontinuities along a wheel-engaging surface thereof; a plurality of vibration-sensitive transducers mounted on the rail for developing initial electrical signals having frequencies representative of the velocity of a car moving along the rail; signal combining means for combining said initial signals to develop a control signal having a frequency representative of car speed; control means for actuating the car retarder between braking and released conditions in response to variations of the control signal frequency above and beLow a critical frequency representative of a given release velocity; said control means including a low-frequency signal channel for actuating the retarder to released condition and having a gate incorporated in said low-frequency channel; and timed application circuit means, connected to said signal combining means and to said gate in said control means, for actuating said gate to closed condition, in response to said control signal, to maintain the car retarder in braking condition for a predetermined limited time interval every time a car approaches the retarder along said rail, regardless of the frequency of said control signal, said time interval being long enough to assure at least limited braking of any car entering the retarder above a preselected minimum speed.
 2. A railway car retarder control system according to claim 1 in which said timed application circuit comprises a timing capacitor, a main charging circuit for charging said timing capacitor to a voltage of given polarity and predetermined amplitude, and squelch switching means for connecting said timing capacitor to said gate in said low-frequency channel each time a control signal is initiated.
 3. A railway car retarder control system according to claim 2, in which said timed application circuit further comprises an auxiliary charging circuit for charging said timing capacitor to a voltage of opposite polarity, and in which said control means includes additional switching means, actuated by said low-frequency signal channel, for connecting said auxiliary charging circuit to said timing capacitor whenever the car retarder is released by operation of said low-frequency signal channel, to preclude a timed reapplication of the car retarder to braking condition on a car that accelerates within the retarder after being braked below said release velocity.
 4. A railway car retarder control system according to claim 2, in which said main charging circuit has a long recharge time, of the order of 20 seconds, to further preclude a timed reapplication of the car retarder on a stalled car.
 5. A railway car retarder control system according to claim 2, in which said main charging circuit is energized in response to the initial electrical signal from the first of said transducers located at the entrance end of the car retarder and is deenergized in the absence of said initial electrical signal from said first transducer.
 6. A railway car retarder control system according to claim 5, in which said main charging circuit has a short charging time period of the order of less than 1 second.
 7. A railway car retarder control system according to claim 6, in which said main charging circuit comprises reset switching means for connecting said timing capacitor to a voltage supply of said given polarity and a reset amplifier having an input connected to said first transducer and an output connected to said reset switching means for actuation thereof, said reset switching means having an actuation time shorter than the actuation time for said squelch switching means by at least said charging time period.
 8. A railway car retarder control system according to claim 5, in which said timed application circuit further comprises an auxiliary charging circuit for charging said timing capacitor to a voltage of opposite polarity, and in which said control means includes additional switching means, actuated by said low-frequency signal channel, for connecting said auxiliary charging circuit to said timing capacitor whenever the car retarder is released by operation of said low-frequency signal channel, to preclude a timed reapplication of the car retarder to braking condition on a car that accelerates within the retarder after being braked below said release velocity. 